1. Field
The present disclosure relates generally to the field of semiconductor device manufacturing and, more particularly, to removal of surface passivation such as from a copper layer following chemical mechanical planarization processes.
2. Description of the Related Art
Electrical interconnects in electronic devices often comprise copper (Cu), due to the resistivity, frequency capability, power requirement and/or electromigration performances of copper. For example, three-dimensional structures can be formed in dielectric material on a substrate surface (e.g., trench and/or via structures). Copper can be subsequently deposited over and/or within the three-dimensional structures to form the desired electrical interconnects.
Chemical mechanical planarization (CMP) is typically used for etching back excess copper on a substrate surface, as patterning of copper using reactive ion etching (ME) may be challenging due to difficulty in the formation of volatile copper-containing byproducts. Chemical mechanical planarization can be used to remove excess copper from the substrate surface (e.g., copper deposited over the substrate surface for forming electrical interconnects) and/or to planarize copper on the substrate surface to prepare the substrate surface for subsequent processing. Chemical mechanical planarization can utilize a combination of chemical and mechanical forces in its removal of material from the substrate surface. For example, chemical mechanical planarization typically uses a polishing pad to apply a slurry solution to a substrate surface for etch back and planarization of the substrate surface. However, exposure of copper to the slurry solution during the chemical mechanical planarization process may result in formation of a passivation film on the substrate surface over the copper. While the passivation film may prevent oxidation of the underlying copper, for example due to exposure of the copper to oxygen-containing ambient during transport of the substrate during processing, the passivation film may undesirably modify one or more characteristics of the substrate surface for subsequent processing.
Use of a plasma process in removal of the passivation film may undesirably modify one or more characteristics of the copper surface. Plasma processes may damage the copper surface, generate contaminants within the reaction space, and/or undesirably modify surface characteristics of one or more other materials on the substrate surface (e.g., a dielectric material, such as a low-k dielectric material). Controlled exposure of the substrate surface to reactants in removal processes that utilize liquid phase reactants may be difficult. Use of liquid phase reactants may also contribute to reduced throughput, for example due to an additional drying process that is required after removal of the passivation material. Additionally, liquid phase reactants may undesirably penetrate pores of porous low-k materials, contributing to degradation of the low-k materials.
Therefore, a continued need exists for improved methods of removing surface passivation material formed over copper.